Value engineering is not uncommon in HVAC. Engineers conduct value engineering exercises to save the initial cost of a new HVAC system. Although some people use value engineering as a cover to cut the specifications of HVAC systems, there are still legitimate ways to save costs.
Here are 10 value engineering ideas to legitimately save cost on new HVAC systems:
- Replace Butterfly Duct Fittings with End Caps
- Omit the Use of Pressurization Riser Ducts
- Increase the Height of Rectangular Ducts
- Replace Aluminium Grilles with GI Grilles
- Use Free Return Instead of Ducted Return
- Change Chilled Water Pipes from Class B to Class C
- Reduce the kA Rating of Circuit Breakers
- Change from Using EF/OC Relay to ELR
- Locate the Control Panel Indoor Instead of Outdoor
- Replace BTU Meters with Flow Meters and Temperature Sensors
To make a value engineering exercise successful, we must recognize that consultants (design engineers) may be over-specifying the materials used in HVAC. At the same time, we also need to be aware that some contractors (project engineers) may reduce costs for the sake of profits.
Furthermore, we also need to recognize that junior design engineers may simply copy and paste the specifications used in previous projects due to a lack of guidance. Hence, they provide an opportunity for contractors to carry out value engineering.
Meanwhile, junior project engineers may be instructed by their boss to simply use value engineering as an excuse to reduce the specifications of the materials used in the project without realizing that such a method of cost savings will hurt the long-term performance of the HVAC system.
Hence, I will elaborate on 10 value engineering ideas that are commonly used in the HVAC industry to cut costs. My intention is to bring awareness to you and let you understand the implication of each idea. With that said, let’s dive into it.
1. Replace Butterfly Duct Fittings with End Caps
Consultants often design HVAC ductwork with butterfly duct fittings because they provide a smoother flow of air during separations.
Butterfly duct fittings are used when two ducts are branching out from one duct. A butterfly duct fittings can also act as a reducer.
At the construction site, rectangular ducts are often delivered in incomplete pieces. HVAC duct workers need to assemble them using duct fittings. Hence, workers need to spend time assembling the butterfly duct fittings as well.
On the other hand, two ducts can simply branch out from one duct without any duct fittings. In fact, many ducts are branched out by means of a direct connection. Meaning, workers cut a hole in the main duct to connect the branch duct.
Once the branch duct is connected, the end of the main duct is capped with a piece of metal. Such a method is known as end cap.
As you can see, without a butterfly duct fitting, workers don’t have to spend time assembling the fittings. Work progress can be improved and thus, operating costs can be reduced.
A typical 30-storey office tower with a VAV HVAC system can have up to 1000 butterfly duct fittings. If the saving of one butterfly duct fitting is $20, the total cost saving of replacing all butterfly duct fittings with end caps can be $20k.
Not to mention, butterfly duct fittings are harder to fabricate than straight ducts. Hence, there are more cost-savings at the production level.
However, the downside of using duct end caps when branching is higher static loss.
Obviously, not allowing the air to flow through smooth corners will increase the overall resistance. But, this problem can be mitigated by installing a guide vane at each branch duct.
Although guide vanes will improve the static loss, we must check back the external static pressure of the air handling unit (AHU) or fan to ensure that the air can be delivered to the farthest diffuser or grille.
If the external static pressure of the AHU or fan is more than sufficient, replacing butterfly duct fittings with end caps can drastically improve the work progress of HVAC ductwork and save costs for the contractor.
2. Omit the Use of Pressurization Riser Ducts
Especially in high-rise buildings, staircase and lift lobby pressurization systems often use masonry shafts to deliver outdoor air from the fan room to dedicated floors.
Usually, the masonry shafts are constructed with bricks with a layer of plaster on the external surfaces. Then, some shafts are built with an internal riser duct to prevent air leakages.
However, the staircase and lift lobby pressurization system of some buildings doesn’t have a riser duct in the masonry shafts. It simply uses the masonry shaft to deliver the outdoor air to pressurize spaces.
Obviously, material and installation costs are reduced significantly when the pressurization riser ducts are omitted. However, some design engineers are concerned about the air leakage rate.
Most of the time, air leakages in masonry shafts are due to improper plastering work. Often, the wall in between risers is the one that is leaking.
Contractors can perform a smoke test to visually see where are the leaking spots and have the respective party fix the problem before commencing a full commissioning work.
In addition, consultants can specify an additional layer of plastering work on the inner surface of the masonry shaft if necessary to further prevent air leakages. However, the potential cost savings will be reduced.
Besides, some pressurization masonry shafts are built with reinforced concrete (RC). With RC, air leakages are minimal and a riser duct is almost unnecessary.
A typical pressurization riser duct may have a duct size of 1000 x 300 mm. If the cost of a riser duct is $25 per square meter, the savings from a 200 meters tall riser duct is $13k.
If you’re a consultant, omitting pressurization riser ducts can save costs for the client. If you’re a contractor, work can progress faster with fewer ducts.
3. Increase the Height of Rectangular Ducts
Rectangular ducts are often cheaper than round ducts (round rigid ducts, not round flexible ducts). Strategically increasing the height of rectangular ducts can further reduce the material cost.
The cost of a duct is based on the total surface area of the duct and the total surface area of a duct is depending on the size of the duct.
For instance, both a 1000 x 300 mm duct and a 650 x 400 mm duct is suitable for an airflow rate of 3500 cfm at 0.1 in.WG per 100 ft. Thus, the total surface area is 2.6 square meters and 2.1 square meters respectively.
If the cost of a duct is $25 per square meter, there is a $12.5 difference in cost between a 1000 x 300 mm duct and a 650 x 400 mm duct with the latter being cheaper.
In a typical construction project, HVAC ducts are preferred to be as low height as possible due to the limited height above the ceiling. However, not all ducts are sized in the most cost-optimized way.
Usually, we need to visit the site during the construction to see the actual space available above the ceiling. Then, we need to coordinate with other services to accommodate for the “taller” duct in order to save duct material costs.
To find the most cost-optimized duct size, we need to check the surface area of different duct sizes to compare. Generally, square-shaped ducts have the lowest cost.
However, square ducts are usually not practical. So, you may need to spend more time checking other sizes and this leads to your work productivity issues.
I also find it very difficult to optimize all duct sizes. Hence, I create a Cost-Optimized Duct Sizing Chart to aid my value engineering work. It is very useful. So, check it out.
In the future, projects may use software like Autodesk Revit to produce 3D views. By then, the potential of such a cost-saving method will decline.
Nevertheless, there are many different duct sizes in a project. If you pay attention, you will always find duct sizes that are waiting to be optimized.
4. Replace Aluminium Grilles with GI Grilles
GI (galvanized iron) grilles are cheaper than aluminium grilles. But, they are more prone to corrosion. Furthermore, they are heavier than aluminium grilles.
However, strategically using GI grilles can lead to significant cost savings, up to 30% per grille.
For example, if the grilles are exposed under the ceiling, GI grilles are suitable because the humidity level is controlled by the air conditioning system. Usually, the space above the ceiling is very humid.
A typical aluminium grille can cost about $10 more than a GI grille. If a project has 2000 pieces of grilles, the potential cost saving is $20k.
Sometimes, only clients with a limited budget will accept this change. Hence, many consultants still prefer to use aluminium grilles and contractors need to be cautious when proposing such a change.
5. Use Free Return Instead of Ducted Return
The return air of air handling units (AHUs) and fan coil units (FCUs) can be either a free return or a ducted return. As the name suggests, a ducted return means the return air goes back to the AHU or FCU by means of a return air duct.
On the other hand, a free return means that there is no return air duct involved. Instead, the return air goes back to the AHU or FCU through a ceiling plenum or a room plenum.
I covered 4 different types of HVAC plenums in my post 4 Types of HVAC Plenums (Basics & Applications).
Basically, we can utilize the space above the ceiling as a plenum for the AHUs and FCUs to return air. So, we simply install return air grilles on the ceiling, without connecting them to any duct. Then, the AHUs and FCUs will create a negative pressure within the ceiling plenum which draws the air back to them through return grilles.
Obviously, a significant amount of cost can be saved from not having to duct most of the return air back to the respective HVAC unit. However, this method of cost savings must be adopted carefully.
The primary reason to use a ducted return is to achieve a balanced return air thereby providing a balanced cooling to every room that is served by the same air conditioning unit.
Hence, ducted returns are necessary for AHUs and FCUs that are serving multiple rooms at the same time. Besides, if they are located far away from the rooms they serve, a ducted return is also needed.
Contrarily, if the AHUs and FCUs are only serving one big room and are located near to the room they serve, a free return is feasible.
However, large air conditioning units are not recommended to use a free return because return grilles that are closer to them can create a loud noise since the return airflow can’t be balanced.
Apart from not having to fabricate and install a return air duct, using free return instead of ducted return also eliminates the need for a return air plenum box. This further adds up to the overall cost savings.
Moreover, by eliminating the return air plenum box, more space can be saved and AHU rooms size can be reduced which, allows the client to have more valuable space for commercial purposes.
6. Change Chilled Water Pipes from Class C to Class B
Normally, the material used for chilled water pipes from 20 mm to 150 mm is carbon steel to BS 1387 Class C. By changing the material from Class C to Class B, the cost of each chilled water pipe can be saved by roughly 10%.
BS 1387 Class C pipes have a greater wall thickness than BS 1387 Class B pipes. By reducing the wall thickness, the lifespan of the chilled water pipes is reduced when the water velocity remains unchanged.
Reducing water velocity can prolong the lifespan of chilled water pipes. Below is the recommended chilled water velocity by Carrier:
Usually, we design chilled water pipe sizes using a water velocity of not more than 10 fps (feet per second). If you want to prolong the lifespan of the pipe, use a lower water velocity.
See my post How to Size Chilled Water Pipe? (Friction Loss Chart) for more about friction loss, water velocity and chilled water pipe sizing.
Nevertheless, changing from Class C to Class B for chilled water pipes is a viable option to reduce cost. If you negotiate the price with pipe suppliers, they usually propose the same.
7. Reduce the kA Rating of Circuit Breakers
The kA rating of circuit breakers is known as the current breaking capacity of circuit breakers. If the short circuit current (amp) exceeds the kA rating of the circuit breaker, the circuit breaker can be damaged.
While it is important to have the right kA rating for circuit breakers, we must recognize that the kA rating can sometimes be too high for HVAC applications.
Many suppliers don’t actually know how to calculate the required kA rating. In fact, many people use previous projects or a rule of thumb to decide the kA rating for MCBs and MCCBs.
Normally, we use 25kA for a 50A MCCB and 16kA for a 25A MCCB. The change of the kA rating of circuit breakers with such sizes is more significant and impactful in terms of cost savings.
If you notice that you’re using a 50A MCCB with 50kA, try to discuss with the supplier and understand why the proposed kA rating is so high.
A typical 50A MCCB is about 30% cheaper when the kA rating is reduced from 25kA to 16kA. Hence, if it is applicable, try to reduce the kA rating of circuit breakers if you desperately need to save cost.
8. Change from Using EF/OC Relay to ELR
EF/OC or earth fault overcurrent relay is more expensive than ELR or earth leakage relay. Although EF/OC relays are better than ELRs, sometimes it is not necessary to go for an EF/OC relay. An ELR will do just fine.
If you are dealing with small fans and air conditioners, an ELR is more than sufficient to do the job. Often, suppliers will tell you that putting an EF/OC relay is overkilling.
Even for an AHU with 11 kW of power supply, an ELR or ELCB is sufficient for electrical protection. Meanwhile, EF/OC relays are usually used to protect high-voltage transformers.
9. Locate the Control Panel Indoor Instead of Outdoor
Strategically placing the control panel of HVAC equipment can save you cost from not having to use higher specifications to withstand outdoor weather.
Most of the time, the cheapest version of a control panel is a wall-mounted type indoor panel with a single door. For the more expensive weatherproof panel, it is usually floor-mounted with a double door to prevent rainwater from entering the panel.
Although equipment such as exhaust fans and pumps can be installed outdoor, their control panel may not necessarily need to be exposed to the weather.
Instead, try to find a room for the control panel so that it stays indoors. For instance, you can install a fan control panel inside a staircase or a domestic cold water pump room.
However, be cautious not to locate the control panel too far away from the equipment or else, the cost of wiring will exceed the benefit of making the panel indoor.
10. Replace BTU Meters with Flow Meters and Temperature Sensors
BTU meters are essentially the combination of flow meters and temperature sensors. BTU is calculated based on water flow rate and temperature differences.
A single unit of BTU meter is much more expensive than a flow meter plus two temperature sensors. For instance, a BTU meter is about 3 times the cost of a flow meter plus two temperature sensors.
However, you need a PLC or some sort of programmable board to create a formula or an algorithm to calculate BTU based on the data from flow meters and temperature sensors.
Although this is not an easy way to save cost, it is a viable option if you really need to tighten up your belt.
This article was originally published on aircondlounge.com. Actions will be taken for unauthorised republication of this article.